Protection spark gap



I A 8, 1951 M. F. D. BOCKMAN EIAL 2,565,945

PROTECTION SPARK GAP Filed Sept. 20, 1949 //7 venf 0/15. War/us F Q fickman Patented Aug. 28, 1951 PROTECTION SPARK GAP Marius F. n. Biickman and Svend Aa. Viirts,

Ludvika, Sweden,

assignors to Allmanna Svenska Elektriska Aktiebolaget,

Vasteras,

Sweden, a Swedish corporation Application September 20, 1949, Serial No. 116,841 In Sweden Novemher'lil, 1948 For the protection of electrical plants or parts of plants against incidental over-voltages, protective spark gaps can be used in combination with automatic circuit-breakers in such a way that in case of flash-over in one or several of the gaps, due to over-voltages, suitable relays automatically may give rise to definite or timelimitedoften very short-term--disconnection of the part in question. Then the are created at the flash-over in the gap will be extinguished, and the part of the plant will be ready for normal function when the' voltage is connected again.

Such a gap should have a Well-defined and constant ignition voltageas well as a steadily burning arc, created at the flash-over, which will not cause appreciable voltage peaks across the gap after the first ignition voltage peak. In the case of an alternating current, for instance, this should be the case without the are having to be re-ignited every half cycle by an ignition voltage of the same magnitude as the first ignition voltage peak, as such repeated voltage peaks would damage the part of the plant intended to be protected. Finally, it is also desirable that the arc created in the gap should be limited in its geometrical extension, thereby reducing the necessary space around the gap, and facilitating an eflicient shielding of the gap within reasonable dimensions, permitting the mounting of the gap outdoors without any risk of altering the ignition voltage due to precipitation or smoke or dust.

The present invention refers to a spark gap in air which fulfills the requirements mentioned above, and which is characterized by the fact that the electrodes and the conductors leading to them are arranged and shaped in such a way that the flash-over is initiated between metal surfaces, the form and distance of which determine the flash-over voltage, and then, the are created at the flash-over is immediately, by the electromagnetic and/or thermal forces of the current brought to such a position that it burns between surfaces of a material suitable as basepoint of the are, for instance of graphite.

The invention will be further described with reference to the accompanying drawing which shows two difierent embodiments of the invention, in Figs. 1 and 2, and in Fig. 3 the practical arrangement of a gap according to Fig. 2.

In the gap according to the form shown in Fig. l, the conductors are designated by l and 2 and the electrodes by 3 and 4, the latter being made of a metal suitable for the purpose. The

(2 Claims. (Cl. 313325 )v electrodes are shapedin, such a manner that a well-defined ignition voltage will be obtained. On the top the electrodes are provided with auxiliary electrodes 'SQan'd'li' of a material, forv instance graphite, which is not only suitable as a'base-point' for strong arcs duri'ngseveral s.ec-" onds without being materially damaged but which will also, under the influence of the are emit so many ions that thearc will. burn continuously, i. e. withoutflbeing extinguished. at possible zero passages of tlie. current. The electrodes will be'. arranged in, such manner that the breakdown will always begin betweenthe main electrodes} and 4., whereby a well-defined ignition voltage will be obtained. The conductors are, however, drawn insuch a way that the arc, by the elec'tro-iiia gnetic forces of the current, is'immedi'ately forced to ascend to the auxiliary electrodes 5 and 6, whereby the main electrodes will be spared and obtain practically no burns, at the same time as the stability of the arc is maintained by the material of the auxiliary electrodes. The thermal arc-currents, produced by the heat production of the arc in the shown embodiment, also contribute to the rapid ascending of the arc to the auxiliary electrodes.

In the form shown in Fig. 1 the arc is forced, at arcing times exceedin 0.1 seconds, to a considerable height and to a considerable extent, 7, and the space necessary for such a gap will be rather large. It is also difiicult to shield or in other way protect it against precipitation and soiling when mounted outdoors.

This drawback is eliminated by the embodiment shown in Fig. 2, where the numerals 1-6 correspondto those of Fig. 1, but where a third auxiliary electrode 1 is placed right above one of the two other auxiliary electrodes, and is in electrical contact with the other one of these electrodes. The principle is here that when the arc starts its ascending movement owing to the electro-magnetic and thermal forces of the current, it will very soon strike the third auxiliary electrode 1. As the latter is in connection with the electrode 6, the Whole current will now pass between the electrodes 5 and l, and the electrode 6 will no more be touched by any arc. In this position, however, the arc cannot be affected by any electro-magnetic forces, because the conductors to the electrode 1 are drawn symmetrically on each side of the conductor 1, and the arc will now stabilize itself in the position 8, shown in the figure. To this fact the ascending thermal aircurrents further contribute, which currents now of course are flowing in the longitudinal direction of the arc.

A spark gap according to the principle of Fig. 2 has the advantage of a relative small space demand, as the geometrical xtension of the arc is very limited. Such a gap therefore may be easily enclosed in a suitable casing of conducting or insulating material to prevent soiling.

A practical design of such a gap in a casing shown in Fig. 3. The numerals 1-7 are the'same as in Fig. 2. The casing is provided with ventilation apertures 9 at the top and ID at the bottom, but forms may be used with an entirely enclosed gapwithout those openings.

W claim as our invention:

1. A spark gap comprising two main electrodes spaced to constitute a calibrated protective gap, one auxiliary electrode connected to and located directly upon each one of said main electrodes, conductors leading to said main electrodes and so arranged and located that the foot points of the are between the main electrodes are moved upwardly to the auxiliary electrodes by electromagnetic and thermal forces, a third electrode located above and spaced from the auxiliary electrode connected to one of said main electrodes, and at least two parallel conductors connectin said thirdv electrode to the conductor leading to the other of said main electrodes, said conductors from the third electrode to the said main electrode being symmetrically displaced around the gap between the third electrode and the said auxiliary electrode in order to avoid any substantial electro-magnetic forces on the are between these electrodes.

2, A spark gap comprising two main electrodes spaced to constitute a calibrated protective gap,

one auxiliary electrode connected to and located directly upon each one of said main electrodes, conductors leading to said main electrodes and so arranged and located that the foot points of the are between the main electrodes are moved upwardly to the auxiliary electrodes by electromagnetic and thermal forces, a third electrode located above and spaced from the auxiliary electrode connected to one of said main electrodes, a casing enclosing the spark gap, and at least two parallel conductors connecting said third electrode to the conductor leading to the other of said main electrodes, said conductors from th third electrode to the said main electrode being symmetrically displaced around the gap between the third electrode and the said auxiliary electrode in order to avoid any substantial electro-magnetic forces on the are between these electrodes, and said conductors forming part of the said casing enclosing the spark gap.

MARIUS F. D. BCSCKMAN. SVEND AA. vORTs.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,069,310 Wurts Aug. 5, 1913 2,230,727 Partington Feb. 4, 1941 2,355,490 Wayman Aug. 8, 1944 FOREIGN PATENTS Number Country Date 25,657 Great Britain Nov. 24, 1903 450,178 Great Britain July 13, 1936 

